This invention relates to a CD-ROM drive, more particularly to a CD-ROM drive and its control method, which can make an optimal control of the spindle motor with a digital circuit at searching.
As shown in FIG. 1, a conventional CD-ROM drive includes a pick-up 1 for detecting data recorded in a CD-ROM by directing laser beams onto the CD-ROM rotated by a spindle motor 6, a high frequency amplification and pick-up servo part 2 for amplifying the high frequency signals received from the pick-up 1 and for making servo operations to control position of a lens in the pick-up 1, a digital signal processing and linear velocity servo part 3 for digital processing the high frequency signals amplified in the high frequency amplification and pick-up servo part 2 to decode the signals into original information and generating acceleration/deceleration control signals DIR-CLV and driving extent control signals PWM-CLV, an error correction part 5 for processing error correction of the decoded signals received from the digital signal processing and linear velocity servo part 3, and applying the error corrected signals to a computer(not shown), a spindle motor driving part 7 for computing driving voltage using the acceleration/deceleration control signals DIR-CLV and the driving extent control signals PWM-CLV received from the digital signal processing and linear velocity servo part 3 and applying the driving voltage to the spindle motor 6, and a microcomputer 4 for controlling the above various parts.
Operation of the CD-ROM drive of FIG. 1 having foregoing system is to be explained hereinafter, referring to FIGS. 2 and 3.
First, when the pick-up 1 reads in recorded information from a CD-ROM by directing a laser beam onto the CD-ROM rotated by the spindle motor 6, the high frequency amplification and pick-up servo part 2 amplifies a high frequency signal received from the pick-up 1 so that the signal has a predetermined gain, and, on the same time, makes a servo operation for controlling position of the lens in the pick-up 1.
In this instant, the digital signal processing and linear velocity servo part 3 digital processes the high frequency signal amplified in, and received from the high frequency amplification and pick-up servo part 2 to decode the signal into an original signal, and the error correction part 5 makes an operation of an error correction algorithm proper to the CD-ROM to correct errors in the decoded signal, and applies the error corrected signal to a computer(not shown).
And, the digital signal processing and linear velocity servo part 3 makes an operation of an output of the high frequency amplification and pick-up servo part 2, and generates a acceleration/deceleration control signal DIR-CLV and a driving extent control signal PWM-CLV for controlling direction of rotation and driving extent of the spindle motor 6.
That is, in controlling the spindle motor 6, a PWM(Pulse Width Modulation) method is used for improvement of efficiency and reduction of heat generation of the spindle motor driving part 7 wherein the acceleration/deceleration control signal DIR-CLV as shown in FIG. 2A, a signal for controlling whether to accelerate or decelerate the spindle motor 6, accelerates the spindle motor 6 at high voltage of the control signal and decelerates the spindle motor 6 at low voltage of the control signal, and the driving extent control signal PWM-CLV as shown in FIG. 2B, a signal for controlling an extent of drive, becomes into a high voltage condition at every cycle of the pulse width modulation carrier and maintains the high voltage condition for a duration proportional to the driving extent.
Accordingly, the longer the duration of the high voltage condition of the driving extent control signal, the more the extent of acceleration or deceleration in a direction corresponding to the acceleration/deceleration control signal DIR-CLV.
And, the microcomputer 4 controls the above parts while the foregoing operations are made.
In the meantime, in case when the pick-up 1 should be moved from a particular spot to another spot of the CD-ROM for searching operation, the microcomputer 4 should move a slide for moving the pick-up 1 to a desired position, and on the same time, in order to satisfy a characteristic of constant linear velocity of a CD-ROM, the microcomputer 4 should accelerate rotation of the spindle motor 6 when the pick-up 1 is to move from an outer circumference to an inner circumference of the CD-ROM, and should decelerate rotation of the spindle motor 6 when the pick-up is to move from an inner circumference to an outer circumference of the CD-ROM.
In this case, a method is used that controlling rotation of the spindle motor 6 using a particular part(frame sync in most cases) of a signal extracted by the pick-up 1. However, since the spindle motor 6 can not be reached to a normal rotation speed within a short time even though the constant linear velocity CLV is automatically controlled after the slide is moved, the spindle motor 6 should be enforced to accelerate or decelerate to reach to the normal rotation speed within a short time.
When the foregoing operation is an operation in a searching shown in FIGS. 3A to 3F, the operation is to be explained referring to wave patterns of driving voltage DM and GFS(Guaranteed Frame Sync) of the spindle motor 6.
Being an output signal of the high frequency amplification and pick-up servo part 2 processed in, and output from the digital signal processing and linear velocity servo part 3, the GFS at high voltage indicates the spindle motor 6 is rotating in the normal speed, and the GFS at low voltage indicates the spindle motor 6 is rotating in a speed faster or slower than the normal speed.
That is, FIGS. 3A to 3C indicate cases when the spindle motor 6 is accelerated when the pick-up 1 is searching the CD-ROM while moving from an outer circumference to an inner circumference, and FIGS. 3D to 3F indicate cases when the spindle motor 6 is decelerated when the pick-up 1 is searching the CD-ROM while moving from an inner circumference to an outer circumference.
Herein, FIGS. 3A and 3D indicate cases when the spindle motor 6 is properly accelerated or decelerated for a duration of search(TK or TB) so that the GFS reaches to high voltage right after finishing the search, cases when the acceleration and the deceleration are done properly.
And, FIG. 3B indicates a case when the acceleration lacks, FIG. 3C indicates a case when the acceleration is excessive, FIG. 3E indicates a case when the deceleration lacks, and FIG. 3F indicates a case when the deceleration is excessive, respectively.
And, alike the GFS in FIGS. 3A and 3D, the GFS in FIGS. 3B, 3C, 3E, and 3F indicate cases when high voltage is not reached at once but after delay for a certain period of time.
However, even if the searching has been finished, the GFS does not reach to high voltage at once but reaches after a certain duration of driving of the spindle motor 6 for compensating the lack or excess.
Therefore, the conventional CD-ROM drive has problems in that it can not carry out the searching operation which is an important function of the CD-ROM within a short time because the duration in which GFS reaches to high voltage after finish of the searching is delayed if an appropriate acceleration or deceleration operation is not made.
That is, even though the conventional CD-ROM drive has its spindle motor accelerated or decelerated during the searching period of time based on experimental data(duration of acceleration or deceleration) for accomplishing a short access time period, in cases when the CD-ROM is changed or a weight deviation of the CD-ROM is great, since the experimental data is not applicable anymore, rotation of the spindle motor can not be controlled appropriately.